NOTE: for tesseract to work, the tiff file you're running it on needs to be renamed to end in .tif (not .tiff) AND it needs to be an image without an alpha channel. If you've renamed the file and tesseract is still barfing, this is probably the problem. Use an image conversion utility with the ability to remove alpha channels to re-save your image. For bulk image conversion I recommend Imagemagick (it's gpl and runs well on the mac).

to ocr your tiff image, do:

tesseract inputimage.tif outputtext -l eng

and you should get a file called outputtext.txt.

Tesseract can also make use of the libtiff library. (www.libtiff.org)
Without libtiff, Tesseract can only read uncompressed and G3 compressed TIFF files.
This code is a raw OCR engine. It has NO PAGE LAYOUT ANALYSIS, NO OUTPUT
FORMATTING, and NO UI. It can only process an image of a single column and create text from it. It can detect fixed pitch vs proportional text. As of 2.0, Tesseract is fully unicode (UTF-8) enabled, and can recognize 6
languages "out of the box.